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Chapter 6: Problem 19

What is a charge-coupled device (CCD)? Why have CCDs replaced photographic film for recording astronomical images?

Short Answer

Expert verified
A Charge-Coupled Device (CCD) is a light-sensitive electronic device that converts light signals into electronic signals. CCDs have replaced photographic film for recording astronomical images due to their higher sensitivity to light, linear response to light, and ease of digital processing, which enables more accurate and efficient capture, processing, and analysis of astronomical images.

Step by step solution

01

Definition of a Charge-Coupled Device (CCD)

A Charge-Coupled Device (CCD) is a device that is used in digital imaging. It is designed to convert light signals into electronic signals. They are constructed using metal-oxide-semiconductor (MOS) technology and contain a series of capacitors coupled together.
02

Explaining the Working of a CCD

When light hits the CCD, it produces electrical charges at the pixel sites. The amount of charge is proportional to the intensity of light, allowing a CCD to record levels of brightness. The charges at each pixel are then transferred through a controlled shift sequence from capacitor to capacitor, carrying the signal corresponding to each pixel to the edge of the CCD array, where they are then converted into a voltage. In this way, a pattern of voltages that represents the picture that was focussed onto the array can be created.
03

Comparison of CCDs to Photographic Film

CCDs are far superior to photographic film in many ways which have led to them replacing film in several applications, including astronomical imaging. This superiority comes from a range of factors. Firstly, CCDs offer much higher sensitivity to light compared to film, which means they can record fainter objects. Secondly, CCDs have a more linear response to light, improving the accuracy of measurements. Additionally, digital images from CCDs are easy to feed into computers for further processing and analysis, while film needs to be developed and then digitised, a process that can introduce errors.

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Most popular questions from this chapter

Why are radio telescopes so large? Why does a single radio telescope have poorer angular resolution than a large optical telescope? How can the resolution be improved by making simultaneous observations with several radio telescopes?

What is active optics? What is adaptive optics? Why are they useful? Would either of these be a good feature to include on a telescope to be placed in orbit?

Why must astronomers use satellites and Earth-orbiting observatories to study the heavens at X-ray and gamma-ray wavelengths?

The Hobby-Eberly Telescope (HET) at the McDonald Observatory in Texas has a spherical mirror, which is the least expensive shape to grind. Consequently, the telescope has spherical aberration. Explain why this doesn't affect the usefulness of HET for spectroscopy. (The telescope is not used for imaging.)

Obtain a telescope during the daytime along with several eyepieces of various focal lengths. If you can determine the telescope's focal length, calculate the magnifying powers of the eyepieces. Focus the telescope on some familiar object, such as a distant lamppost or tree. DO NOT FOCUS ON THE SUN! Looking directly at the Sun can cause blindness. Describe the image you see through the telescope. Is it upside down? How does the image move as you slowly and gently shift the telescope left and right or up and down? Examine the eyepieces, noting their focal lengths. By changing the eyepieces, examine the distant object under different magnifications. How do the field of view and the quality of the image change as you go from low power to high power?
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